In a dense wavelength division multiplexed (DWDM) system having a high number of signal channels, the initially deployed system typically does not have all of the signal channels fully populated. The number of signal channels that are populated depends upon several factors including the amount of capacity initially required in the DWDM system. To make the amplifiers in the system operational during the lifetime of the system, from initial deployment at less than capacity to full capacity after upgrades, a substitute signal may be used to fill one or more empty channels to maintain the saturation (and other) performance characteristics of the amplifier. In conventional narrowband Erbium doped fiber amplifier DWDM systems, it is theoretically possible for as few as one substitute signal to be used to saturate the amplifier, depending on the operational bandwidth of the substitute signal, although commercial applications employ a substitute signal for each channel.
Raman amplified systems use numerous pump wavelengths to achieve a much larger operational bandwidth than an Erbium doped fiber amplified system. The saturation mechanism for the Raman amplifier is the depletion of the individual pumps. This depletion occurs through pump-pump and pump-signal interactions. As a result, a more delicate balance of substitute signals is used to maintain the system performance of the Raman amplifier. In conventional Raman-amplified systems, a substitute signal is used for each unused signal channel.
As capacity demands continue to grow, efforts are focusing on increasing the usable bandwidth in both EDFA and Raman optical communication systems. As the number of channels increases, the cost associated with providing a substitute signal laser for each channel rises in tandem. Accordingly, it would be desirable to provide systems and methods for maintaining amplifier saturation (and system performance) at reasonable prices as the available bandwidth increases.